The field of the present invention relates to optical fiber. In particular, apparatus and methods are described herein for launching an optical signal into multimode optical fiber.
Multimode optical fiber (MMF) is widely deployed in existing data transmission networks and systems. Transmission speeds (i.e., bandwidth or bit rate) through multimode fibers are typically limited by modal dispersion. In other words, different spatial modes supported by the multimode fiber propagate with different modal group velocities, leading to temporal spreading of an optical signal and limiting the speed at which data may be transmitted along the fiber. Such modal dispersion may be increased by deviations of the multimode fiber radial index profile from an ideal design index profile. Improvements in multimode fiber design and fabrication have resulted in fibers exhibiting reduced modal dispersion. However, there is interest in further increasing the usable bandwidth of such improved multimode fiber, and in increasing the bandwidth of previously-deployed multimode fiber in legacy fiber-optic networks, in which modal dispersion effects have become a limitation on transmission speed.